Documentation/Account and plan
Team and permissions
Staff accounts and access to individual tabs.
You add users in Settings, under Team. Each of them signs in with their own e-mail and password. The owner sees the whole panel; an employee sees only the tabs you switch on - the Settings tab always stays owner-only.
Permissions are set per person, and you define the default set for new employees once. Changing that default does not touch accounts that already exist.
An employee account can be deactivated - access goes, the history of their work stays - or removed entirely. At least one active owner has to remain, so you cannot deactivate your own account.
If adding a user shows a limit message, that is the plan's limit rather than an error. Seats are bought in the Subscription tab.